Bug 27999: Display the description of authorized values category

Bug 27999: Display the description of authorized values category

This patch corrects a parameter in the authorized values template so
that the right value is passed for displaying the description of an
authorized value category.

To test, apply the patch and go to Administration -> Authorized values.

- In the table of authorized values, click on one which has a
  description in the "Description" column.
- On the page titled "Authorized values for category XXX," you should
  see that description under the heading.
- Use the "Show category" dropdown to try some other categories.

Signed-off-by: Séverine QUEUNE <severine.queune@bulac.fr>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>